The present invention relates to control valves of the type for use in construction equipment such as backhoe, skid steers, front end loaders, fluid cranes, etc. In particular, the present invention relates to a fluid control valve having metering which varies with associated valve stroke. The valve provides improved fluid control.
Currently used hydraulic machines such as backhoes, front end loaders, skid steers, hydraulic cranes, etc. use hydraulic control valves to direct the motion of various functions on these machines such as swinging, booming, bucket dipping, and bucket rotation. The metering of these valves allows fine control of the various functions as the associated valve spool is moved to its closed position. There are typically three areas inside of a valve which have metering characteristics. These metering characteristics include open center metering, metering in, and metering out. Open center metering refers to choking off the open center flow of open center type control valves, which generate the pressure to move the associated load. Metering in refers to the metering of hydraulic fluid being metered from the valve into the cylinder, and metering out refers to hydraulic fluid being metered out of the cylinder through the valve.
The typical functions of hydraulic equipment currently use valve timing which is either slightly metered in, neutral or slightly metered out. Typically, valve designers avoid the use of heavy metering in or heavy metering out functions as a result of energy considerations. More specifically, depending upon the amount of metering, energy can be wasted since high metering restrictions usually result in the operation of the hydraulic pump such that the associated driving engine has to generate additional power to force oil through the restrictions associated with heavy metering. However, there are certain functions on hydraulic equipment such as a backhoe which are usually operated at relatively high pressures (e.g. the swinging motors), or have an overrunning load (e.g., the hydraulics associated with a boom) which have the potential to generate pressure appropriate to generate a metering out conditions. Thus, in certain circumstances such as those set out immediately above, it may be advantageous to only have heavy metering out on one side of the valve, thus, producing a non-symmetrical valve.
Most control valves have a spool which has metering notches which meter the flow when there is partial movement of the spool. In its fully open position, the open annulus between the undercut of the spool and the land in the associated spool housing opens up completely, thus effectively eliminating the function of the metering notches on the spool. The problem with this conventional type arrangement of metering notches is that the function of the metering notches is substantially lost when the spool is moved to and beyond the position where the undercut of the spool moves past the land in the associated spool housing. (See prior art FIGS. 1 and 2.)
As discussed above, for certain applications when fluid is released under pressure from a fluid cylinder such as a hydraulic cylinder or hydraulic motor, it is desirable in many applications to meter the flow out of such an actuator such that motion of the actuator is smoothly and/or controllably reduced or terminated. Thus, it would be desirable to provide a control valve operable to release the fluid from an actuator such that the release of fluid is metered throughout substantially the full range of valve motion while still retaining the ability to substantially increase the fluid flow through the valve while maintaining some degree of metering.
The control valve of this invention comprises a valve body which has a work port and an exhaust port. The ports are connected through a valve spool bore which provides fluid communication between the ports. A valve spool moves in the valve spool bore of the valve body to control the communication of fluid between the ports. A plurality of metering notches are spaced circumscriptively around a spool annular land on the valve spool. As the valve spool moves within the spool bore, the metering notches, which can be nested and can vary in length, width, depth and shape, are exposed thereby controlling the amount of fluid passing from one port to the other port.
The present invention provides an alternative embodiment being a variable metering fluid control valve comprises a valve body having at least one work port and one exhaust port with the ports in fluid communication with a spool bore and an exhaust core, said exhaust core having an exhaust core land and a reciprocating valve spool in the spool bore to control communication of fluid between the work port and the exhaust core, with said valve spool having an annular land portion with a plurality of variable length metering notches, wherein the annular land portion of the valve spool remains in contact with the exhaust core land through the full stroke of the valve spool. The variable length metering notches may be nested and may also be varied in width, depth, and cross-section so that precise control of the fluid system is achieved.